Target expansion rate control in an extreme ultraviolet light source

Patent metadata

Field	Value
Publication number	US-9820368-B2
Application number	US-201514824141-A
Country	US
Kind code	B2
Filing date	Aug 12, 2015
Priority date	Aug 12, 2015
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

A method includes providing a target material that comprises a component that emits extreme ultraviolet (EUV) light when converted to plasma; directing a first beam of radiation toward the target material to deliver energy to the target material to modify a geometric distribution of the target material to form a modified target; directing a second beam of radiation toward the modified target, the second beam of radiation converting at least part of the modified target to plasma that emits EUV light; measuring one or more characteristics associated with one or more of the target material and the modified target relative to the first beam of radiation; and controlling an amount of radiant exposure delivered to the target material from the first beam of radiation based on the one or more measured characteristics to within a predetermined range of energies.

First claim

What is claimed is:

1. A method comprising:
providing a target material that comprises a component that emits extreme ultraviolet (EUV) light when converted to plasma;
directing a first beam of radiation toward the target material to deliver energy to the target material to modify a geometric distribution of the target material to form a modified target;
directing a second beam of radiation toward the modified target, the second beam of radiation converting at least part of the modified target to plasma that emits EUV light;
measuring one or more characteristics associated with one or more of the target material and the modified target relative to the first beam of radiation;
analyzing the measured one or more characteristics associated with one or more of the target material and the modified target relative to the first beam of radiation; and
controlling an amount of radiant exposure delivered to the target material from the first beam of radiation based on the analysis of the one or more measured characteristics to within a predetermined range of radiant exposures.

2. The method of claim 1 , wherein measuring the one or more characteristics associated with one or more of the target material and the modified target comprises measuring an energy of the first beam of radiation.

3. The method of claim 2 , wherein measuring the energy of the first beam of radiation comprises: measuring the energy of the first beam of radiation reflected from an optically reflective surface of the target material, or measuring an energy of the first beam of radiation directed toward the target material.

4. The method of claim 2 , wherein measuring the energy of the first beam of radiation comprises measuring a spatially integrated energy across a direction perpendicular to a direction of propagation of the first beam of radiation.

5. The method of claim 4 , wherein directing the first beam of radiation toward the target material comprises overlapping the target material with an area of the first beam of radiation that encompasses its confocal parameter.

6. The method of claim 1 , wherein measuring the one or more characteristics associated with one or more of the target material and the modified target comprises measuring a position of the target material relative to a target position.

7. The method of claim 6 , wherein the first beam of radiation is directed along a first beam axis, and the position of the target material is measured along a direction that is parallel with the first beam axis.

8. The method of claim 6 , wherein measuring the position of the target material comprises measuring the position of the target material along two or more non-parallel directions.

9. The method of claim 1 , wherein measuring the one or more characteristics associated with one or more of the target material and the modified target comprises one or more of:
detecting a size of the modified target before the second beam of radiation converts at least part of the modified target to plasma; and
estimating an expansion rate of the modified target.

10. The method of claim 1 , wherein controlling the amount of radiant exposure delivered to the target material from the first beam of radiation based on the one or more measured characteristics comprises controlling an expansion rate of the modified target.

11. The method of claim 1 , wherein controlling the amount of radiant exposure delivered to the target material from the first beam of radiation based on the one or more measured characteristics comprises determining whether a feature of the first beam of radiation should be adjusted based on the one or more measured characteristics.

12. The method of claim 11 , wherein, if it is determined that the feature of the first beam of radiation should be adjusted, then adjusting one or more of: an energy content of a pulse of the first beam of radiation and an area of the first beam of radiation that interacts with the target material.

13. The method of claim 12 , wherein adjusting the energy content of the pulse of the first beam of radiation includes one or more of:
adjusting a width of a pulse of the first beam of radiation;
adjusting a duration of a pulse of the first beam of radiation; and
adjusting an average power within a pulse of the first beam of radiation.

14. The method of claim 11 , wherein:
directing the first beam of radiation toward the target material comprises directing pulses of first radiation toward the target material;
measuring the one or more characteristics comprises measuring the one or more characteristics for each pulse of first radiation; and
determining whether the feature of the first beam of radiation should be adjusted comprises determining for each pulse of first radiation whether the feature should be adjusted.

15. The method of claim 1 , wherein:
providing the target material comprises providing a droplet of target material;
modifying the geometric distribution of the target material comprises transforming the droplet of the target material into a disk shaped volume of molten metal; and
the target material droplet is transformed into the disk shaped volume in accordance with an expansion rate.

16. The method of claim 1 , wherein directing the first beam of radiation toward the target material also converts a part of the target material to plasma that emits EUV light, wherein less EUV light is emitted from the plasma converted from the target material than is emitted from the plasmas converted from the modified target, and the pre-dominant action on the target material is the modification of the geometric distribution of the target material to form the modified target.

17. The method of claim 1 , wherein:
modifying the geometric distribution of the target material comprises transforming a shape of the target material into the modified target including expanding the modified target along at least one axis according to an expansion rate; and
controlling the amount of radiant exposure delivered to the target material comprises controlling the expansion rate of the target material into the modified target.

18. The method of claim 17 , wherein the modified target is expanded along the at least one axis that is not parallel with the optical axis of the second beam of radiation.

19. The method of claim 1 , wherein:
measuring one or more characteristics associated with one or more of the target material and the modified target comprises measuring an energy of the first beam of radiation directed toward the target material;
controlling the amount of radiant exposure delivered to the target material comprises adjusting an amount of energy directed to the target material from the first beam of radiation based on the measured energy; and
directing the first beam of radiation toward the target material comprises overlapping the target material with an area of the first beam of radiation that encompasses its confocal parameter.

20. The method of claim 19 , wherein adjusting the amount of energy directed to the target material from the first beam of radiation comprises adjusting a property of the first beam of radiation.

21. The method of claim 1 , wherein controlling the amount of radiant exposure delivered to the target material from the first beam of radiation comprises one or more of:
adjusting an energy of the first beam of radiation just before the first beam of radiation delivers the energy to the target material;
adjusting a position of the target material; and
adjusting a region of the

Assignees

• Asml Netherlands Bv

Inventors

• Riggs Daniel Jason
• Rafac Robert Jay

Classifications

• H05G2/0027

  Arrangements for controlling the supply; Arrangements for measurements · CPC title

• H05G2/0088 Primary

  for preconditioning the plasma generating material · CPC title

• H05G2/008 Primary

  involving an energy-carrying beam in the process of plasma generation · CPC title